The long-term goal of this research is to identify molecular targets for new mental health therapeutics, particularly for affective disorders. We will approach this goal by defining cellular mechanisms of acute, estrogen receptor beta (ERbeta)-dependent regulation of synapses in the hippocampus of adult male and female rats. That acute estrogen-ERbeta signaling in the hippocampus plays a critical role in mental health is based on four convergent lines of research: First, fluctuating levels of estrogen in women are associated with changes in memory, mood, and affect. Second, animal studies support a role for estrogen in regulating affective behaviors and indicate that activation of ERbeta in the hippocampus is anxiolytic and anti-depressive. Third, ERbeta agonists delivered directly into the hippocampus can reduce behavioral measures of anxiety and depression rapidly, within 10-20 minutes. Fourth, a key estrogen, 17beta-estradiol (E2), is produced locally in the hippocampus of males and females, providing a physiological source of E2 that could act acutely to influence affective behavior in both sexes. Together, these findings indicate that understanding the mechanisms of acute E2 actions in the hippocampus could point to molecular targets for future, focused efforts to develop new therapies for the treatment of anxiety and depression. Previous studies of acute E2 actions in the hippocampus have concentrated on the postsynaptic elements of synaptic transmission. We recently discovered that E2 acutely potentiates hippocampal excitatory synaptic transmission through at least one, ERbeta-dependent, presynaptic mechanism. We propose to build on these results by investigating the molecular mechanisms of acute E2 regulation of synaptic transmission, explicitly addressing both pre- and postsynaptic mechanisms. We will use a combination of two-photon imaging, whole-cell patch-clamp electrophysiology, synaptic biochemistry, and behavioral studies to pursue three specific aims: 1) To establish whether acute E2-induced synaptic potentiation is pre- and/or postsynaptic; 2) To investigate presynaptic mechanisms of acute E2- induced synaptic potentiation; 3) To test the role of kinases in acute E2 effects on synaptic plasticity and affective behaviors. Because there is evidence that males and females are differentially sensitive to acute effects of E2 on hippocampal physiology, we will study both sexes to investigate how cellular mechanisms of acute E2 action differ between the sexes. Discovery of sex-specific mechanisms of E2 action and their role(s) in behavior could lead to sex-specific treatments for affective disorders.